1. Field of the Disclosure
The present disclosure relates generally to a wireless communication system, and more particularly, to a system and method for logging and reporting information for an averted Radio Link Failure (RLF) in the Minimization of Drive Test (MDT) framework for a 3RD Generation Partnership Project (3GPP) Long Term Evolution (LTE) scheme.
2. Description of the Related Art
Wireless communication systems are widely deployed to provide various types of communication content such as voice and data. Typical wireless communication systems may be multiple-access systems capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power, etc.). Examples of such multiple-access systems include Code Division Multiple Access (CDMA) systems, Time Division Multiple Access (TDMA) systems, Frequency Division Multiple Access (FDMA) systems, Orthogonal Frequency Division Multiple Access (OFDMA) systems, and the like. Additionally, the systems can conform to specifications such as 3RD Generation Partnership Project (3GPP), 3GGP 2 (3GPP2), High Speed Packet Access (HSPA), High Speed Downlink Packet Access (HSDPA), High Speed Uplink Packet Access (HSUPA), 3GPP Long-Term Evolution (LTE), LTE Advanced (LTE-A), etc.
A 3GPP Long Term Evolution (LTE) User Equipment (UE) while in Radio Resource Control (RCC) connected mode can face a Radio Link Failure (RLF), and can declare an RLF on detection of at least one of physical layer problems, random access problem indication from a Medium Access Control (MAC) layer, and an indication from a Radio Link Control RLC that a maximum number of retransmissions has been reached. From a network optimization perspective, whenever the RLF is declared, the UE is expected to record a snapshot of the serving cell measurements along with the measurements of a neighboring cell that is available, so that whenever the UE subsequently reenters a connected mode with the serving cell or any of the neighboring cells, the UE can inform the network regarding the availability of measurements when the RLF was encountered. This process can help in network optimization.
3GPP Minimization of Drive Test (MDT) Work Item has devised a standard procedure of UE storing these measurement information on occurrence of an RLF and reporting the information back to the network the next time that the UE attempts an RRC Connection Re-Establishment procedure or an RRC Connection Establishment procedure. Such RLF information is helpful for a network as it equips operators with real time information from fields from various UEs and assists them to perform improved network planning.
FIG. 1 illustrates a timing graph of a UE facing an RLF over a period of time according to a use case. The timing graph is obtained based on signal samples received by the UE at different instances of time while moving through a coverage hole or tunnel. The signal samples indicate the strength of the signal received by the UE from the network at different time periods. The UE has a particular threshold signal strength set for initiating monitoring of an RLF. If the signal strength of the signal sample received by the UE goes below the threshold, the UE identifies that the UE initiates monitoring an RLF situation. In a similar manner, the UE sets a certain signal strength upon reaching a certain signal strength measurement and the UE declares that an RLF has occurred.
According to FIG. 1, the UE moves through a tunnel or coverage hole. While entering the tunnel, the signal strength of the signal sample is noted. As the UE moves through the tunnel, it can be observed that the signal strength of the signal samples decreases as the UE moves towards the center of the tunnel. At a certain point in the tunnel, the signal strength goes below the threshold and the UE initiates monitoring of the signal samples for an RLF situation. The UE records measurements of the signal strengths of the samples at pre-determined time intervals. At a certain time period the UE observes a measurement that shows that the UE is about to face an RLF but recovers. It is referred to as a “near radio link failure” situation. The UE may temporarily experience loss of synchronization but recovers in time before reaching a condition to declare an RLF is met. As the UE has recovered before the RLF occurred, the UE does not record the measurements of the service cell and its neighboring cells.
In an initial deployment scenario, the UE initiates the RLF monitoring procedure, but before it faces an RLF, the UE might recover. But per the procedure, the UE will not record measurements and report them. It should be noted that a UE in a slow moving vehicle may encounter an RLF. Hence even information related to a near RLF situation is helpful to the network.
In LTE specifications R12/R13 it is expected that there will be a dense deployment of small cells and it will alter the UE geometry due to the heterogeneous network deployment in the field. Thus, information regarding weak network coverage areas may be required by operators for optimizing configuration parameters for an improved end user experience.
Thus, there is a need for a procedure to capture near RLF information when UEs face temporary synchronization failures and recover before declaring an RLF.